Connected: An Internet Encyclopedia
RFC 792 - Parameter Problem Message

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### Parameter Problem Message

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |     Code      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Pointer    |                   unused                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Internet Header + 64 bits of Original Data Datagram      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       IP Fields:

       Destination Address

          The source network and address from the original datagram's data.

       ICMP Fields:

       Type

          12

       Code

          0 = pointer indicates the error.

       Checksum

          The checksum is the 16-bit ones's complement of the one's
          complement sum of the ICMP message starting with the ICMP Type.
          For computing the checksum , the checksum field should be zero.
          This checksum may be replaced in the future.

       Pointer

          If code = 0, identifies the octet where an error was detected.

       Internet Header + 64 bits of Data Datagram

          The internet header plus the first 64 bits of the original
          datagram's data.  This data is used by the host to match the
          message to the appropriate process.  If a higher level protocol
          uses port numbers, they are assumed to be in the first 64 data
          bits of the original datagram's data.

       Description

          If the gateway or host processing a datagram finds a problem with
          the header parameters such that it cannot complete processing the
          datagram it must discard the datagram.  One potential source of
          such a problem is with incorrect arguments in an option.  The
          gateway or host may also notify the source host via the parameter
          problem message.  This message is only sent if the error caused
          the datagram to be discarded.

          The pointer identifies the octet of the original datagram's header
          where the error was detected (it may be in the middle of an
          option).  For example, 1 indicates something is wrong with the
          Type of Service, and (if there are options present) 20 indicates
          something is wrong with the type code of the first option.

          Code 0 may be received from a gateway or a host.

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Connected: An Internet Encyclopedia
RFC 792 - Parameter Problem Message